The application of polyester resin and fiberglass onto a spirally rotating mandrel is a new method of making pipes and tanks having a diameter of up to 9 feet or more. Since the fiberglass reinforced polyester tanks and pipes are new arrivals on the market, the technology for making such articles is not highly developed.
Resin is normally deposited on a spirally rotating mandrel by transfer with a roller from a resin box or by spraying the resin through nozzles onto the surface of the rotating mandrel. Use of resin boxes precludes the use of chopped fiberglass for the chopped fiberglass would stick to the roller and fall into the box. As a consequence, rolls of more expensive fiberglass mats are used. Spraying resin through nozzles cannot be used with resins filled with particulate materials, such as inorganic fillers because the filler can become lodged in the nozzle and the flow of resin is restricted.
Fiberglass rovings that contain many individual strands of fiberglass are available commercially at a much lower price than fiberglass mats. Choppers for these rovings are also known that can chop the rovings to pieces of various lengths.
It is an object of the present invention to provide a convenient and inexpensive method of building a fiberglass reinforced polyester lamination on a spirally rotating mandrel.